The present invention relates to compositions of free-radical polyethylene and ethylene/.alpha.-olefin copolymers and to the application of these compositions to the manufacture of films, to the sheathing of telephonic cables, and to the manufacture of retractable housings.
European Pat. No. 0,052,889 describes the application of a coating to a substrate at a temperature of at least 232.degree. C. The coating has a thickness less than 12.5 .mu.m and is made of 20 to 98 weight percent polyethylene obtained under high pressure and having a specific gravity lower than 0.93 and a melt index between 4 and 6.3 dg/min; and from 2 to 80 weight percent of at least one ethylene/.alpha.-olefin copolymer. The .alpha.-olefin has from 3 to 8 carbon atoms. The copolymer has a melt index between 0.5 and 100 dg/min, a polydispersity index (defined by the ratio Mw/Mn of the weight-average molecular weight to the number-average molecular weight) between 2.7 and 4.1, a total unsaturation ratio between 0.1 and 0.3 double bonds per 1000 carbon atoms, and a specific gravity between 0.912 and 0.940.
French Pat. No. 2,481,709 describes a mixture comprising: (a) from 30 to 80 weight percent of an ethylene/.alpha.-olefin copolymer having from 3 to 12 carbon atoms, the copolymer having a specific gravity lower than 0.945 and an instrinsic vicosity, measured at 135.degree. C., of between 1.7 and 10 dl/g; and (b) from 20 to 70 weight percent polyethylene obtained under high pressure, which has a specific gravity of between 0.915 and 0.935 and an intrinsic vicosity, measured at 135.degree. C., lower than 1.3 dl/g. An intrinsic vicosity, measured at 135.degree. C., higher than 1.7 dl/g for an ethylene/.alpha.-olefin copolymer, corresponds to a melt index (measured according to standard specification ASTM D 1238-73) lower than 0.3 dg/min.
U.S. Pat. No. 3,176,052 describes a homogeneous mixture comprising: (a) from 5 to 75 weight percent of a polyethylene obtained by a free-radical mechanism, having a specific gravity between 0.91 and 0.94; and (b) from 25 to 95 weight percent of an ethylene/.alpha.olefin copolymer with a specific gravity higher than 0.92 and a melt index between 0.1 and 10 dg/min. This patent shows that the improvement of the gloss of an extruded film obtained from such a mixture, compared with extruded films obtained from each constituent of the mixture, is more pronounced with higher melt index (from 3 to 10 dg/min according to the examples) of the polyethylene obtained by a free-radical mechanism and higher with lower melt index (from 0.5 to 1.4 dg/min, according to the examples) of the copolymer.
Extruded films are also known that are prepared from polyethylene obtained by a radical mechanism and which have a thickness of at least 20 .mu.m.